Electric fuses for igniting explosive charges



ELECTRIC FUsEs FOR ICNITING EXPLOSIVE CHARGES May 30, 1961 vovow ,986,099 Patented May 3G, 1961 'ELECTRIC FUSES FOR IGNTING EXPLOSIVE CHARGES Ernst H. Doerpinghaus, Heilwigstrasse 6, Hamburg, Germany Continuation of application Ser. No. 506,230, May 5, 1955. This application Dec. 8, 1958, Ser. No. 778,764

Claims priority, application Switzerland Aug. 23, `1954 8 Claims. (Cl. 102-28) The present invention relates to fuses for igniting explosive charges.

More particularly, the present invention relates to electric fuses which are provided with an ignitable material which is ignited by a spark in the fuse.

Conventional fuses of this type have several disadvantages particularly with respect to the assembly of the components thereof.

One of the objects of the present invention is to provide a fuse of the above type which can be very easily assembled.

Another object of the present invention is to provide a fuse of the above type composed of simple rugged elements which are inexpensive to manufacture and which will operate reliably.

With the above objects in view the present invention includes in a fuse for igniting an explosive charge, a casing of tubular configuration having an end wall and having an open end portion distant from this end wall. An electrically non-conductive body is located within this casing at the open end portion thereof, and the electrically nonconductive body is formed with an opening passing there-V through and extending substantially along the axis of the casing. This body has an inner tubular surface which defines the opening of the body, an annular end surface `directed toward and spaced from the end wall of the casing, and an outer tubular surface surrounding the inner tubular surface and located closely adjacent to the wall of the casing at the open end -portion of the latter. These surfaces of the electrically non-conductive body, which may be made of a ceramic material, are covered with an electrically conductive coating and the coating at the outer surface of the body is in direct engagement with the wall of the casing at the open end portion of the latter. An electrode is located in the opening of the electrically nonconductive body and engages the coating at the inner surface of this body so as to close the opening thereof, and an ignitable material is located within the casing between the electrically non-conductive body and the end wall of the casing. The casing itself forms a second electrode so that a circuit may be completed between these electrodes and the electrically conductive coating, so that Vthe latter will act as a resistance for the purpose of igniting the material within the casing.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

Fig. l shows in a longitudinal sectional view taken axially through the fuse of the invention the structure of the fuse which is shown in Fig. l mounted in position at a part of the cartridge which carries the explosive charge, the structure being shown in Fig. l on an enlarged scale of approximately 10:1; and

Fig. 2 shows in a fragmentary cross sectional view at a still larger scale the construction of the non-conductive body at the junction between the coated inner tubular and annular end surfaces thereof.

The fuse of the present invention includes a tubular metallic casing 8, and this tubular casing 8 has an end Wall 11 formed with an opening 12 passing therethrough, This opening 12 communicates with the explosive charge 15. The opening 12 is closed by a sheet 13 of any suitable material which is capable of maintaining the interior of the casing 8 closed at the opening 12 thereof and which at the same time will give way to the ignited material within the casing so that a flame may project through the opening 11 in order to ignite the charge 15. The ignitable material 9 in the form of a suitable powder or the like is located within the casing 8 next to the end wall thereof,

An electrically non-conductive body 1 is located within the casing 8 at an open end portion of the latter which is distant from its end wall 11. This body 1 is formed with an opening 2 passing therethrough along the axis of the casing 8, and the body 1 has an inner tubular surface 4 defining the opening f2, an annular end surface 4 spaced from and directed toward the end wall 11, and an outer tubular surface 4" located closely adjacent to the wall of the casing 8 at the open end portion of the latter. These surfaces 4, 4', and 4" of the body 1 are coated with an electrically conductive metallic coating, and the metallic coating at the surface 4 is directly in engagement with the surface of the wall of the casing 8 at the open end portion of the latter. The coating at the annular end surface 4' is directly in engagement with the ignitable material 9, and an electrode 6, 7 is located within and closes the opening 2 of the body 1, this electrode 6, 7 being in engagement with the coating at the inner tubular surface 4 of the body 1.

lThe electrode 6, 7 and the casing 8 which forms a second electrode are adapted to be located in an electrical circuit which will provide a ow of electricity through the coating on the body 1 so that this coating acts as an electrical resistance for igniting the material 9 within the casing 8.

The body 1 is made of a ceramic material which can be ground during the manufacture of the body 1 so that it can be very accurately manufactured. The exterior surfaces of the body 1, which is to say the surfaces 4, 4, and 4", as Well as the annular end 'surface 3 are all coaxial with respect to each other, the surfaces 4 and 4" being substantially cylindrical.

As may be seen particularly from Fig. 2, the junction 5 between the inner tubular surface 4 and the annular end surface 4 of the body 1 has an extremely small radius r, this radius r being much smaller than the radius of curvature of the lbody 1 at the junction 16 between the annular end surface 4' and the outer tubular surface 4" of the body 1. The coating on the body 1 has a thickness at the junction 5 between the surfaces 4 and 4 which is substantially less than the thickness of the rest of the coating. Also, it will be noted fromV Fig. 1 that the top end of the electrode 6, 7 as viewed in Fig. l, terminates short of the top end of the body 1 so that the upper end of the opening 2 is not occupied by the electrode 6, 7 and forms a recess in which the ignitable material 9 is located, so that the annular junction 5 is covered with the material 9.

The coating on the ceramic body 1 is formed by applying a metal salt solution to the latter or by dipping the body 1 into such a solution, this being a solution of platinum compounds, for example. After such application of the solution to the body or dipping of the body into the solution, the solution which remains on the body is dried under moderate heat so as to leave on the exterior surface of the body the metal from the solution, and when a coating of desired thickness is obtained this coating is sintered to the body for providing a reliable bond between the coating and the ceramic body. The coating which covers the annular surface 3 is removed by grinding, although, if desired, the coating need not be removed from the Surface 3 so that in 'this case the coating at this surface will act as a shunt to prevent undesired electrical ignition by static electricity, for example.

The ceramic body is repeatedly dipped and dried in the above manner so that the thickness of the coating can be increased in this way, and the dipping and drying is repeated until a coating of desired thickness is obtained. Because of the sharpness of the edge of the body at the junction 5 the coating of electrically conductive material which is formed in this way on the body 1 is necessarily thinner at the junction 5 than at any other part of the coating. Therefore, the resistance at the junction 5 is at maximum, and the coating will melt first at the junction 5 to provide at this junction the spark which ignites the material 9.

The casing 8 is formed intermediate its ends with an indentation 14, shown in Fig. 1, so that when the body 1 is introduced into the casing the indentation 14 will determine the location of the body 1 within the casing. Also, the sheet 13 need not be used if the end wall 11 of the casing 8 is constructed in such a way that it will open at the place where the opening 11 is located. For example, the wall 11 may be made thinner at the region of the opening 12 than at other parts so that the pressure of the ignited material 9 will break through the wall at the place where the opening 12 is shown in Fig. l.

It will be noted from Fig. l that the opening 2 of the body 1 has a minimum diameter between the ends of the opening 2 and the diameter of the opening 2 gradually increases from the point of minimum diameter toward the opposite ends of the openingV 2, with this point of minimum diameter being located nearer to the bottom end of the member 1, as viewed in Fig. 1. Thus, the electrode 6, 7 will have the portion 7 longer than the portion 6, and the latter has a sharper conical surface, as is evident from Fig. l. The exterior tubular surface 4" is bevelled next to the end surface 3 of the body 1, and the casing 8 has its open end pressed inwardly as shown at in Fig. 1 so as to tightly hold the member 1 within the casing 8.

The electrical circuit for passing current through the electrically conductive coating includes in addition to the electrode 6, 7 the casing 8 which forms a second electrode connected to the electrically conductive p-artof the cartridge, as indicated in Fig. 1. A contact 17 engages the electrode 6, 7 this contact l17 being insulated by a sleeve 18 of the gun, and the contact 17 is connected electrically with a generator 19 which is also connected electrically with the casing 8 through the electrically conductive part of the cartridge, as shown diagrammatically in Fig. 1.

vThis application is a continuation of co-pending application Serial No. 506,230, led May 5, 1955, now abandoned, and entitled Electric Fuses for Igniting Explosive Charges.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of fuses differing from the'types described above.

While the invention has been illustrated and describedV as embodied in electric fuses, it is not intendedV to be limited to the details shown, since various modifications-and structural changes may be made withoutdeparting in any way from the spiritof the present invention.

Without further analysis, the foregoing will so fully reveal-the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, `fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended l to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

l. A fuse for igniting an explosive charge, comprising, in combination, an electrically non-conductive' tubular body having an inner tubular surface defining an openingV passing through said body, an outer tubular surface surrounding said Vinner tubular surface, and a pair of opposed annular end surfaces interconnecting said inner and outer tubular surfaces; an electrically conductive coating covering said inner and outer tubular surfaces and one of said end surfaces of said body, said coating having a vminimum thickness at the junction between said inner tubular surface and said one end surface; an electrode locatedA in said opening of said tubular body against the portion of the coating which covers said inner tubular surface thereof and closing said opening of said body; a hollow electrically conductive casing containing an ignitable Vmaterial and having an open end portion and a closed end, said body being located in and closing said open end portion of said casing and having the portion of said coating which covers said outer tubular surface of said body in engagement with an inner surface portion of said casing and the one coated end surface being in contact with the ignitable material, said casing forming a second electrode so that when current flows between said electrodes the metal coating will melt at said junction at which the coating has a minimum thickness and a maximum resistance to provide at this junction a spark which serves to ignite the material in said casing.

2. A fuse for igniting an explosive charge, comprising,

in combination, an electrically non-conductive tubular body having an inner tubular surface dening an opening passing through said body, an outer tubularsurface' surrounding said inner tubular surface, and a pair of opposed annular end surfaces interconnecting said inner and outer tubular surfaces; an electrically conductive coating covering said inner and outer tubular surfaces fand one of said end surfaces of said body, said coating having a minimum thickness at the junction between said inner tubular surface and said one end surface; an le':lectrode located in said opening of said tubular body against the portion ofthe coating which covers said inner tubular surface thereof and closing said opening'of said body; V'a hollow electrically conductive casing containing an ignitable material and having an open end portion and a closed end, said body being located in and closing said open ed portion of said casing and having the portion of said coating which covers said outer tubular surface of said body in engagement with an inner surface portion of saidcasing and the one coated end surface being in contactwith the ignitable materiaLsaid casing forminga second electrode so that when current ows between said electrodes the metal coating will melt at said junction at which the coating has a minimum thickness and a maximum resisty ance to provide at this' junction a spark which serves to coaxial.

3. An electric fuse for igniting an explosive charge, comprising, in combination, aV ceramic body formed with an opening passing therethrough and having an inner tubular surface defining said opening, an outer tubular surface surrounding said inner tubular surface, and a pair of opposed annular end surfaces extending between said inner and outer tubular surfaces; an electrically conductive coatingcovering said inner and outer tubular surfaces and one of said end surfaces, said coating having a minimum thickness at the junction between said inner tubular surface and said one end surface; an electrode located in said opening of said Vceramic body against the coating which covers said inner tubular surface thereof and closing said opening; and a casing containing an ignitable material and having an open end portion in which said body is located and a closed end, said body closing said open end portion of said casing and having the coated annular end surface located in said casing and in contact with the ignitable material, said casing being electrically conductive and engaging the coating which covers the outer tubular surface of said body, said casing forming a second electrode so that when current ows through said electrodes and coating the metal coating will melt at said junction at which the coating has a minimum thickness and a maximum resistance to provide at this junction a spark which serves to ignite the material in the casing.

4. A fuse for igniting an explosive charge, comprising, in combination, an electrically conductive tubular casing having a closed end and an open end portion distant from said closed end; an electrically non-conductive cylindrical body of substantially the same diameter as said open end portion and located in said casing at said open end portion thereof, said body being formed with an aperture passing longitudinally therethrough and located substantially along a longitudinal axis of said casing, and said body having an inner tubular surface defining said aperture passing longitudinally therethrough, annular end surfaces, and an outer tubular surface located next to said tubular casing; an electrically conductive coating covering said inner and outer tubular surfaces and one of said annular end surfaces, the coating having a minimum thickness at the junction between said inner tubular surface and the one coated annular end surface of said body; and an electrode in said longitudinal aperture of said body against said coating and closing said opening, said casing engaging said coating at the outer tubular surface of said body so that the open end portion of said casing is closed, said casing having an ignitable material located therein between the one coated annular end surface of said body and said closed end of said casing, said casing serving aS a second electrode so that when current ows between the electrodes and said coating the metal coating will melt at said junction at which said coating has a minimum thickness and a maximum resistance to provide at this junction a spark which serves to ignite the material in said casing, so that ignition of the material in the casing will take place in the regon of said junction.

5. A fuse for igniting an explosive charge, comprising, in combination, an electrically conductive tubular casing having a closed end and an open end portion distant from said closed end; an electrically non-conductive cylindrical body of substantially the same diameter as said open end portion and located in said casing at said open end portion thereof, said body being formed with an aperture passing longitudinally therethrough and located substantially along a longitudinal axis of said casing, and said body having an inner tubular surface defining said aperture passing longitudinally therethrough, annular end surfaces, and an outer tubular surface located next to said tubular casing; an electrically conductive coating covering said inner and outer tubular surfaces and one of said annular end surfaces, the coating having a minimum thickness at the junction between said inner tubular surface and the one coated annular end surface of said body; and an electrode in said longitudinal aperture of said body against said coating and closing said aperture, said casing engaging said coating at the outer tubular surface of said body so that the open end portion of said casing is closed, said casing having an ignitable material located therein between the one coated annular end surface of said body and said closed end of said casing, said casing serving as a second electrode so that when current ows between the electrodes and said coating the metal coating will melt at said junction at which said coating has a minimum thickness and a maximum resistance to provide at this junction a spark which serves to ignite the material in said casing, so that ignition of the material in the casing will take place in the region of said junction, the junction between said inner tubular surface and the one coated annular end surface of said body having a radius of curvature substantially smaller than the radius of curvature at the junction between said outer tubular surface and said coated annular end surface of said body.

6. A fuse for igniting an explosive charge, comprising, in combination, a tubular casing having a closed end and an open end portion distant from said closed end, said casing being electrically conductive and adapted to contain an ignitable material; an electrically non-conductive cylindrical body of substantially the same diameter as said open end portion and located in said casing at said open end portion thereof spaced from said closed end thereof and formed with an aperture passing longitudinally therethrough and extending substantially along a longitudinal axis of said casing, said body having an inner tubular surface defining said aperture, annular end surfaces, and an outer tubular surface located closely adjacent to said tubular casing; an electrically conductive coating covering said inner and outer tubular surfaces and one of said annular end surfaces of said body and engaging the wall of said casing at said open end portion thereof, said coating having a minimum thickness at the junction between said inner tubular surface and said one annular end surface; and an electrode located in said; longitudinal aperture of said body against said coating and closing said aperture, said electrode terminating short of said one coated annular end surface of said body so as to form a recess in the aperture of said body at an end of said aperture which is nearest to said closed end of said casing, whereby the ignitable material in the casing will be located in said recess, said casing acting as a second electrode so that when current flows through said electrodes said coating will melt at said junction at which the coating has a minimum thickness and a maximum resistance to provide at this junction a spark for igniting the material in the casing.

7. A fuse for igniting an explosive charge, comprising, in combination, a tubular casing having a closed end and an open end portion distant from said closed end; an electrically non-conductive cylindrical body of substantially the same diameter as said open end portion and located in said casing at said open end portion thereof and formed with an aperture passing longitudinally therethrough and extending substantially along a longitudinal axis of said casing, said aperture having a minimum diameter between its ends and gradually increasing in diameter from the portion of minimum diameter toward the ends of said aperture, said body having an inner tubular surface defining said aperture, annular end surfaces, and an outer tubular surface located closely adjacent to said tubular casing; an electrically conductive coating covering said inner and outer tubular surfaces and one of said annular end surfaces, said coating having a minimum thickness at the junction between said inner tubular surface and said one annular end surface; and an electrode located in and closing said aperture, said electrode also engaging said coating and having a configuration which mates with that of said aperture so that said electrode has a minimum diameter between its ends and gradually increases in diameter from said portion of minimum dia-meter toward said ends thereof, whereby said electrode cannot be removed from said opening without being deformed, said casing serving as a second electrode so that when current ows through said electrodes, said coating will melt at said junction at which the coating has a minimum thickness and a maximum resistance to provide at this junction a spark for igniting an ignitable material located in said casing between said closed end thereof and said body.

8. A fuse for igniting an explosive charge, comprising, in combination, a tubular casing having a closed end and an open end portion distant from said closed end; an electrically non-conductive cylindrical body of substans tially the same diameter as said open end portion and lo cated in said casing at said open end portion thereof and being formed with an `aperture passing longitudinally therethrough and extending valong a longitudinal axis of said casing, said body having an inner surface defining said aperture, annular end surfaces One of which is directed toward and spaced from said closed end of said casing, and an outer surface located next to the tubular casing, said outer surface of said body being bevelled at an end portion thereof distant from said one end surface of said body; an electrically conductive coating covering said inner and outer surfaces and said one annular end surface and having a minimum thickness at the junction between said inner surface and said one annular end surface, said coating engaging the wall of said casing li at said open end portion thereof, said casing also being bevelled and engaging said coating at the bevelled portion of said Outer surface of said body as well as at the remainder of said outer surface of said body; and an electrode located in and closing the aperture of said body,

References Cited Vin the le of this patent i UNITED STATES PATENTS 2,079,690

Grisdal .V Mayfll, 1937 2,645,701 Y Kerridg'e et-al. July 14, 1953 FOREIGN PATENTS A 13,618 France c Y May 19, 1911 914,022 France June 11, 1946 967,649 France Mar. 29, 1950 

